This invention relates in general to a resistor, the resistance of which may be precisely controlled, and more particularly, to a radiation sensitive resistor whose resistance is precisely controlled at a constant value by means of a digitally programmable voltage source.
Many electrical circuits have parameters which must be calibrated by varying the value of electrical components in the circuit. Thus, in a multi-channel magnetic tape recorder, it is often desirable to calibrate the resistance of each signal processing channel in order to effect equalization between the signals in the multiple channels. Calibration of the resistors in each of the several recorder channels may be effected by manually varying the resistance of each resistor by means of a tool such as a screwdriver. Manual calibration is disadvantageous because it is slow, difficult to effect in inacessible locations, labor intensive, and expensive. Moreover, if the circuit component to be calibrated is remotely located, calibration may be virtually impossible. Thus, there is a need for a resistor which may be calibrated easily, quickly, and inexpensively, even when the resistor is part of a circuit which is in a remote or inaccessible location. With the widespread digital control of electronic equipment, it is also desirable that calibration of the resistors in an electronic circuit be compatible with digital techniques.